By the mid-1980s, Lewis had begun to write for television series; his writing credits include episodes of Perfect Scoundrels, Taggart, The Bill, Wycliffe, Inspector Morse, Kavanagh QC, The Ambassador, Monsignor Renard, Playing the Field, Without Motive, The Last Detective, Murphy's Law, Spooks and Lewis. Lewis has co-written three of the Sharpe films, Sharpe's Battle, Sharpe's Challenge and 2008's Sharpe's Peril. He also penned several episodes of Cadfael and an episode of Hornblower.